This invention relates to a loading and unloading airlock for a vacuum treatment chamber to be provided in communication with the vacuum treatment chamber in which thin films are formed on substrates or in which the thin films on the substrates are subjected to hyperfine processing.
Generally in an in-line vacuum treatment apparatus, a loading airlock for substrates is directly connected in communication with an inlet side of a vacuum treatment chamber in which thin films are formed on substrates, or in which the thin films on the substrates are subjected to hyperfine processing, and an unloading airlock is directly connected in communication with an outlet side of the vacuum treatment chamber. These loading and unloading airlocks are provided to load and unload the substrates to and from the vacuum treatment chamber without impairing the vacuum inside the vacuum treatment chamber and are arranged such that the pressure inside those chambers can be alternated between a vacuum and atmospheric pressure.
A conventional loading and unloading airlock apparatus is constructed as shown in FIGS. 10 through 13. In these figures the loading and unloading airlock apparatus is provided with a lock chamber 1. A transporting inlet 4 is provided on one side of the walls of the lock chamber 1, and a transporting outlet 5 on the opposite side. On the outer edge of the inlet 4, an inlet valve member 11 to be opened and closed by means of an opening and closing mechanism 10 comprising, for example, a rack 7 to be reciprocated by a cylinder 6, and a rotatable shaft 9 integrally formed with a gear 8 to be rotated by the rack 7, is arranged to be seated, thereby closing the transporting inlet 4. On the inner edge of the transporting outlet 5, an outlet valve member 17 to be opened and closed by means of an opening and closing mechanism 16 comprising, for example, a rack 13 to be reciprocated by a cylinder 12, and a rotatable shaft 15 integrally formed with a gear 14 to be rotated by the rack 13, is arranged to be seated, thereby closing the transporting outlet 5.
The transporting inlet 4 and the transporting outlet 5 are provided with openings which are longer in the vertical direction. A substrate holder 3 on which substrates are detachably mounted is transported into and out through the openings in a vertically upright posture by fixing the lower end thereof to a long substrate holder support 23, thereby enabling the holder 3 to move together with the substrate holder support 23. A total of four wheels 24 are provided on the sides of the front and rear ends of the substrate holder support 23. A rack bar 22 is provided on the lower side of the substrate holder support 23 by holding it there with a spring (not shown).
Inside of the lock chamber 1, there is provided a transport mechanism 18. This transport mechanism 18 comprises, for example, a pinion gear 21 fixed to a rotatable shaft 20 which is rotated by a rotating mechanism (not shown) and a pair of parallel rails 25, 25. When the pinion gear 21 is rotated in mesh with the rack bar 22, the wheels 24 of the substrate holder support 23 are moved on the rails 25, 25, thereby transporting the substrate holder 3.
A gas inlet port 26 is provided in an upper plate which forms a chamber wall of the lock chamber 1. An exhaust port 27 is provided in a horizontal bottom plate which forms another chamber wall.
Further, as shown in FIG. 13, a gas introduction pipe 30 having a gas introduction shutoff valve 28 and a gas flow regulating valve 29 is connected to the gas inlet port 26 of the lock chamber 1. A gas exhaust pipe 33 having a gas exhaust shutoff valve 31 and a gas exhaust speed regulating valve 32 is connected to the gas exhaust port 27 of the lock chamber 1.
The conventional loading and unloading airlock apparatus is constructed as described above and does not have a means of regulating the flow of gas inside the lock chamber 1. There was a problem in that gas turbulences occur inside the lock chamber 1 when the lock chamber 1 is brought back to atmospheric pressure by introducing a gas into the chamber 1 through the gas introduction pipe 30 or, in the reverse, when the chamber 1 is evacuated through the gas exhaust pipe 33. Such gas turbulence can cause the dust particles which have accumulated inside vacuum chamber 1 to be agitated and adhere to the substrates 2. The adhesion of dust particles is not desirable because the dust particles adhered to the substrates 2 will be a hindrance in forming thin films on the substrates 2 or subjecting the films on the substrates to hyperfine processing, thereby giving rise to inferior products.
In order to prevent the adhesion of dust particles, the lock chamber 1 is conventionally returned to atmospheric pressure by slowly introducing a gas therein or is slowly evacuated so that no gas turbulences occur inside the chamber There was a disadvantage in that, since it took a long time to perform gas introduction or gas exhausting, the treatment efficiency could not be increased. Further, since the bottom plate on which the gas exhaust port 27 is provided is horizontal, it has been found that, when chamber 1 is evacuated, swirls occurred in a space in the neighborhood of the inlet to the gas exhaust port 27, and that the dust particles in the neighborhood of the gas exhaust port 27 are raised by the swirls and can adhere to the substrates 2.
Table 1 given below shows the quantity of dust particles of 0.5 micron and over in diameter which adhered to a 5-inch wafer when a lock chamber 1 of about 1,000 liters in volume was evacuated.
TABLE 1 ______________________________________ Method of Timing of Quantity of exhausting exhausting dust particles ______________________________________ quick 40 seconds for 1,000-5,000 pcs exhausting vacuum chamber pressure to change from 760 Torr to 0.2 Torr slow 10 minutes for 1,000-3,000 pcs exhausting vacuum chamber pressure to change from 760 Torr to 0.2 Torr slow 8 hours for 10-100 pcs exhausting vacuum chamber pressure to change from 760 Torr to 0.2 Torr ______________________________________
The object of this invention is to solve the conventional problems and disadvantages and to provide a loading and unloading airlock apparatus which enables evacuation of the lock chamber and return thereof back to atmospheric pressure in a shorter time and to decrease the quantity of dust particles adhering to the substrates.